Radio communication systems, such as paging systems, are well known in the art. Conventional paging systems often include multiple transmitters for transmitting radio frequency signals at various geographic sites. Typically, a paging terminal/controller included in the paging system receives message information from data entry devices or from conventional wired telephones via a telephone network, such as the public switched telephone network. After a predetermined time period, or after a specified amount of message information has been collected, the paging terminal/controller encodes the message information into selective call messages utilizing a suitable paging format, such as GSC (Golay Sequential Code) or POCSAG (Post Office Code Standardization Advisory Group). The paging terminal/controller then enables all or a selected group of the transmitters utilizing an "enable" signal and subsequently provides the selective call messages to the enabled transmitters. When transmission of the messages is complete, the paging terminal/controller disables the transmitters to indicate that all of the messages have been transmitted. The transmitters thereafter modulate the messages for transmission over predetermined RF channels. The messages are subsequently received by radio communication devices, such as pagers, carried by system subscribers.
To ensure that system subscribers miss as few messages as possible, some conventional paging systems further include a redundant transmitter, which serves as a replacement for a transmitter that is non-functional for one reason or another, e.g., power to the transmitter is lost or the transmitter is under repair. When it is switched in to replace the non-functional transmitter, the redundant transmitter monitors the link to the paging terminal/controller to await detection of the next-transmitted enable signal with which the paging terminal/controller enables, or "keys up", the transmitters. In response to reception of the next enable signal, the redundant transmitter modulates and transmits the subsequently provided messages over the RF channel utilized by the non-functional transmitter. In this manner, the system subscribers which would normally receive messages from the non-functional transmitter instead conveniently receive messages from the redundant transmitter.
Subscribers to a paging system utilizing this replacement method, however, can still miss messages when a transmitter ceases functioning after being keyed up, i.e., enabled. In this situation, any encoded messages which follow the provided enable signal are lost because the redundant transmitter is not able to transmit any messages until after reception of the next enable signal provided by the paging terminal/controller. This problem is especially severe in paging systems in which messages collected over a large period of time or a large number of messages are provided to the transmitters in a single long transmission following an enable signal. In this situation, subscribers can be out of service for a long period of time while the redundant transmitter waits for reception of a subsequent enable signal.
Thus, what is needed is an improved method, in a paging system, for replacing a transmitter which has ceases functioning. This method should ensure that system subscribers do not miss selective call messages which would normally have been transmitted by the non-functioning transmitter.